The goal of this project is to define structural and functional aspects of CTD kinases that are critical for HIV replication. They are CycT1:CDK9 (P-TEFb), CycL1/L2:CDK11, CycK:CDK12 and CycK:CDK13. P-TEFb is the co-activator of NF-kB and Tat. CDK11 and CDK12 play critical roles in HIV 3' end formation, i.e. cleavage and polyadenylation. CDK13 is important for HIV mRNA splicing. Studies of their regulation in cells and in HIV silencing and reactivation are major goals of this proposal. In addition, we are developing sensitive assays for the release of P-TEFb from its inactive 7SK snRNP in cells, which will be adapted for the analysis of compounds that can be used to reactivate HIV from latency as well as treat many different forms of cancer and inflammation. These studies will inform all strategies aimed at reducing and/or eliminating the reservoir of HIV in infected individuals.